Led array package

ABSTRACT

Various aspects of a light emitting apparatus includes a substrate. Various aspects of the light emitting apparatus include a light emitting die arranged on the substrate. The light emitting die includes one or more side walls. Various aspects of the light emitting apparatus include a reflective die attach material extending along the one or more side walls of the light emitting die.

BACKGROUND Field

The present disclosure relates generally to vertical LEDs and, moreparticularly, to vertical LEDs having light output that is similar tothe light output by lateral LEDs.

Background

Solid state light emitting devices, such as light emitting dies (LEDs),are attractive candidates for replacing conventional light sources suchas incandescent, halogen, and fluorescent lamps. LEDs have substantiallylonger lifetimes than all three of these types of conventional lightsources. In addition, some types of LEDs now have higher conversionefficiencies than fluorescent light sources and still higher conversionefficiencies have been demonstrated in laboratories. Finally, LEDscontain no mercury or other potentially dangerous materials, therefore,providing various safety and environmental benefits.

Several different LED designs exist today, including vertical LEDs andlateral LEDs. Vertical LEDs have been considered as a replacement forlateral LEDs in array packages because vertical LEDs perform better thanconventional lateral LEDs. However, simply using a vertical LED as a“drop-in” replacement for a lateral LED produces a 20% lumen drop inmost LED chip-on-board configurations due to the occurrence of lightabsorbing effects between LEDs. Therefore, it is difficult to usevertical LEDs as a replacement for lateral LEDs without additionaloptimization to account for the lumen drop.

SUMMARY

Several aspects of the present invention will be described more fullyhereinafter with reference to various apparatuses.

One aspect of a light emitting apparatus includes a substrate. The lightemitting apparatus includes a light emitting die arranged on thesubstrate. The light emitting die includes one or more side walls. Thelight emitting apparatus includes a reflective die attach materialextending along the one or more side walls of the light emitting die.

Another aspect of the light emitting apparatus includes a substrate. Thelight emitting apparatus includes a light emitting die arranged on thesubstrate. The light emitting die includes a translucent carriersubstrate.

One aspect of a lamp includes a housing. The lamp includes a lightemitting apparatus coupled to the housing. The light emitting apparatusincludes a substrate. The light emitting apparatus includes severallight emitting dies arranged on the substrate. Each of the lightemitting dies includes one or more side walls. The light emittingapparatus includes a reflective die attach material extending along theone or more side walls of each of the light emitting dies.

BRIEF DESCRIPTION OF THE DRAWINGS

The various aspects of the present invention illustrated in the drawingsmay not be drawn to scale. Rather, the dimensions of the variousfeatures may be expanded or reduced for clarity. In addition, some ofthe drawings may be simplified for clarity. Thus, the drawings may notdepict all of the components of a given apparatus or method.

Various aspects of the present invention will be described herein withreference to drawings that are schematic illustrations of idealizedconfigurations of the present invention. As such, variations from theshapes of the illustrations as a result, for example, manufacturingtechniques and/or tolerances, are to be expected. Thus, the variousaspects of the present invention presented throughout this disclosureshould not be construed as limited to the particular shapes of elements(e.g., regions, layers, sections, substrates, bulb shapes, etc.)illustrated and described herein but are to include deviations in shapesthat result, for example, from manufacturing. By way of example, anelement illustrated or described as a rectangle may have rounded orcurved features and/or a gradient concentration at its edges rather thana discrete change from one element to another. Thus, the elementsillustrated in the drawings are schematic in nature and their shapes arenot intended to illustrate the precise shape of an element and are notintended to limit the scope of the present invention.

Various aspects of apparatuses will now be presented in the detaileddescription by way of example, and not by way of limitation, withreference to the accompanying drawings, wherein:

FIG. 1a illustrates a cross-section view of an exemplary embodiment of avertical LED.

FIG. 1b illustrates cross-section view of a vertical LED havingp-electrode 110 routed to the top of the vertical LED.

FIG. 2a illustrates a plan view of an exemplary embodiment of a lightemitting device.

FIG. 2b illustrates a top level view of an exemplary embodiment of alight emitting device.

FIG. 3 illustrates a cross-section view of an exemplary embodiment of anLED having a die attach material.

FIG. 4a illustrates a cross-section view of an exemplary embodiment ofan LED device.

FIG. 4b illustrates a top level view of an exemplary embodiment of thelight emitting device.

FIGS. 5a-5c are side view illustrations of various exemplary apparatuseshaving a light-emitting device.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of various exemplary embodimentsof the present invention and is not intended to represent the onlyembodiments in which the present invention may be practiced. Thedetailed description includes specific details for the purpose ofproviding a thorough understanding of the present invention. However, itwill be apparent to those skilled in the art that the present inventionmay be practiced without these specific details. In some instances,well-known structures and components are shown in block diagram form inorder to avoid obscuring the concepts of the present invention. Acronymsand other descriptive terminology may be used merely for convenience andclarity and are not intended to limit the scope of the invention.

The word “exemplary” is used herein to mean serving as an example,instance, or illustration. Any embodiment described herein as“exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments. Likewise, the term “embodiment” ofan apparatus, method or article of manufacture does not require that allembodiments of the invention include the described components,structure, features, functionality, processes, advantages, benefits, ormodes of operation.

It will be understood that when an element such as a region, layer,section, substrate, or the like, is referred to as being “on” anotherelement, it can be directly on the other element or intervening elementsmay also be present. In contrast, when an element is referred to asbeing “directly on” another element, there are no intervening elementspresent. It will be further understood that when an element is referredto as being “formed” on another element, it can be grown, deposited,etched, attached, connected, coupled, or otherwise prepared orfabricated on the other element or an intervening element.

Furthermore, relative terms, such as “beneath” or “bottom” and “above”or “top,” may be used herein to describe one element's relationship toanother element as illustrated in the drawings. It will be understoodthat relative terms are intended to encompass different orientations ofan apparatus in addition to the orientation depicted in the drawings. Byway of example, if an apparatus in the drawings is turned over, elementsdescribed as being “above” other elements would then be oriented “below”other elements and vice versa. The term “above”, can therefore,encompass both an orientation of “above” and “below,” depending of theparticular orientation of the apparatus. Similarly, if an apparatus inthe drawing is turned over, elements described as “below” other elementswould then be oriented “above” the other elements. The terms “below”can, therefore, encompass both an orientation of above and below.

It will be further understood that the terms “comprises” and/or“comprising,” when used in this specification, specify the presence ofstated features, steps, operations, elements, and/or components, but donot preclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof. The term “and/or” includes any and all combinations of one ormore of the associated listed items.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by aperson having ordinary skill in the art to which this invention belongs.It will be further understood that terms, such as those defined incommonly used dictionaries, should be interpreted as having a meaningthat is consistent with their meaning in the context of the relevant artand the present disclosure and will not be interpreted in an idealizedor overly formal sense unless expressly so defined herein.

In the following detailed description, various aspects of the presentinvention will be presented in the context of a light-emitting die. Alight-emitting die shall be construed broadly to include any suitablesemiconductor light source such as, by way of example, a light emittingdiode (LED) or other semiconductor material which releases photons orlight through the recombination of electrons and holes flowing across ap-n junction. Accordingly, any reference to an LED or other light sourcethroughout this disclosure is intended only to illustrate the variousaspects of the present invention, with the understanding that suchaspects may have a wide range of applications.

The following description describes a vertical LED array design forreplacing lateral LED array designs. The vertical LED design describedin the foregoing paragraphs provides a light output that is similar toconventional lateral LED arrays. As will be discussed in detail in theforegoing paragraphs, by providing a translucent substrate and areflective die attach material that surrounds the vertical LEDs of anarray, similar light output to conventional lateral LEDs is realized.

FIG. 1a illustrates a cross-section view of an exemplary embodiment of avertical LED 100. An LED is a semiconductor material impregnated, ordoped, with impurities. These impurities add “electrons” or “holes” tothe semiconductor, which can move in the material relatively freely.Depending on the kind of impurity, a doped region of the semiconductorcan have predominantly electrons or holes, and is referred respectivelyas n-type or p-type semiconductor regions.

Referring to FIG. 1, the LED 100 includes an n-type semiconductor region102 and a p-type semiconductor region 105. A reverse electric field iscreated at the junction between the two regions, which cause theelectrons and holes to move away from the junction to form an activeregion 104. When a forward voltage sufficient to overcome the reverseelectric field is applied vertically across the p-n junction through apair of electrodes 101, 106, electrons and holes are forced into theactive region 104 and recombine. When electrons recombine with holes,they fall to lower energy levels and release energy in the form oflight.

In this example, the n-type semiconductor region 102 is formed on agrowth substrate (not shown) and the active layer is formed between then-type semiconductor region 102 and the p-type semiconductor region 105.The p-type electrode 106 is directly or indirectly formed on the p-typesemiconductor layer 105. The growth substrate, on which the n-typesemiconductor layer 102 is formed, is removed so that the patternedn-type electrode 101 can be formed on the surface of the n-typesemiconductor region 102 that was attached to the growth substrate.However, the n-type semiconductor region and the p-type semiconductorregion of this example may be reversed. For instance, the p-typesemiconductor region 105 may be formed on the growth substrate. As thoseskilled in the art will readily appreciate, the various conceptsdescribed throughout this disclosure may be extended to any suitablelayered structure. Additional layers or regions (not shown) may also beincluded in the LED 100, including but not limited to buffer,nucleation, contact and current spreading layers or regions, as well aslight extraction layers.

The n-type semiconductor layer and the p-type semiconductor layer maycomprise gallium nitride. As shown in FIG. 1 below the n-p typesemiconductor layers is a broad area reflective p-type electrode 106,and a thermally conductive substrate 107 to support the device structuremechanically. The p-type electrode reflects light produced by the activelayer 104 so that it is not absorbed by the substrate 107 below. Theconductive substrate may comprise a transparent or translucent materialsuch as silicon or aluminum nitride. Light incident on a translucentsubstrate will be partially passed through and partially absorbed. Byway of example, a translucent substrate supporting a blue LEDencapsulated by a phosphor would pass between 10%-90% of the blue andyellow light with the remaining light being absorbed. In contrast,substantially all light that is incident on a transparent substrate willbe passed through with almost no absorption. An example of a transparentsubstrate is sapphire. As will be discussed in greater detail below,aluminum nitride is preferable over silicon for a translucent substratein chip-on-board LED packages because it absorbs less light thansilicon.

In the vertical LED of FIG. 1a the p-type electrode 106 is formed belowthe n-p semiconductor layers. However, in some aspects of the lightemitting device, it is possible to route the p-electrode to the top ofthe vertical LED structure. FIG. 1b illustrates cross-section view of avertical LED 120 having p-electrode 110 routed to the top of thevertical LED. As shown, both n-electrode 101 and p-electrode 110 areabove the n-p semiconductor layer. Thus, electrical traces can beconnected directly to the n-electrode 110, providing greater flexibilityin designing the vertical LED array of the chip-on-board package.

FIG. 2a illustrates a plan view of an exemplary embodiment of a lightemitting device 200. The light emitting device includes several verticalLEDs 205 having translucent substrates 210. As discussed in thepreceding paragraphs, the translucent substrate may comprise aluminumnitride. The light emitting device also includes a substrate 220 and aphosphor layer 240.

As shown, the vertical LEDs 205 are arranged on the substrate 220. Thesubstrate 220 may be comprised of layers of aluminum, anodized aluminum,silver, and a distributed bragg reflector (DBR). The vertical LEDs 205are also covered by the phosphor layer 240 which scatters some of thelight produced by the vertical LEDs 205. The phosphor layer, which willbe discussed in greater detail with respect to FIG. 2b , may comprisephosphor particles that scatter the light from the vertical LEDs indifferent directions. The scattered light, in some aspects of thedevice, could be redirected to an adjacent vertical LED. If the adjacentvertical LED comprises material that is light absorbing, at least someof the redirected light will be absorbed by the adjacent vertical LED.When light is absorbed rather than output, the device's performancesuffers.

The vertical LEDs 205 in this exemplary figure have a translucentsubstrate 210, which has lower light absorption properties than commonlyused substrate materials such as silicon. Thus, light absorption betweenadjacent vertical LEDs is reduced by the translucent substrate 210leading to better light output from the light emitting device. Forinstance, the translucent substrate may provide a 10% lumen increase inlight output over a conventional silicon substrate. Additionally, thesubstrate may be optically tuned to make the substrate more or lesstranslucent so that the LED array can be further customized fordifferent devices.

FIG. 2b illustrates a top level view of an exemplary embodiment of thelight emitting device 200. The light emitting device includes an arrayof the vertical LEDs 205, the phosphor layer 240, and the substrate 220.As shown, the substrate 220 may be used to support a number of verticalLEDs 205. The phosphor layer 240 may be deposited within a cavitydefined by an annular, or other shaped boundary that extends around theupper surface of the substrate 220. The boundary may be formed by asuitable mold or, alternatively, formed separately from the substrate220 and attached to the substrate using an adhesive or other suitablemeans. The phosphor layer 240 may include phosphor particles suspendedin an epoxy, silicone, or other carrier that may be constructed fromsoluble phosphor that is dissolved in the carrier. As discussed abovewith respect to FIG. 2a , light emitted from each of the vertical LEDs205 may be scattered by the phosphor layer and partially absorbed byadjacent LEDs. However, the translucent substrates 210 of the verticalLEDs 205 partially remedies the absorption issue because it absorbs lesslight than other conventional substrates such as silicon. However, theincorporation of a reflective adhesive material that surrounds thevertical LED may further remedy light absorption issues between verticalLEDs in a chip-on-board package.

FIG. 3 illustrates a cross-section view of an exemplary embodiment of avertical LED 300 attached to a substrate 320 by a die attach material305. The vertical LED 300 includes a translucent substrate 310 asdescribed in detail with respect to FIGS. 1 and 2, and is arranged onthe substrate 320. The die attach material 305 is used to bond thevertical LED 300 to the substrate 320. The die attach material alsocovers at least portion of the side walls 325 of the vertical LED 300.In some aspects of the device, the die attach material may cover aportion of the side wall 325 of the vertical LED 300 that at least halfthe height of the vertical LED. In such aspects, the die attach material305 may cover a portion of the vertical LED 300 that is up to, but notover the active region 104, which was discussed in detail with respectto FIG. 1.

The die attach material increases the light output of vertical LEDsarranged in an array by decreasing light absorption between the verticalLEDs that are arranged close to each other. In some aspects of thedevice, the die attach material may be a white epoxy because white epoxyforms a reflective surface. However, the die attach material may be anyadhesive suitable for bonding the vertical LED to the substrate 320 thatalso has reflective properties. A die attach material that is reflectivemeans that it would reflect more than 50% of incident light. A whiteepoxy die attach material may be preferable in some aspects because itreflects about 80% of blue and yellow light. By limiting lightabsorption further, the reflective die attach material may boost thelight output of a vertical LED array by another 10% lumen (in additionto the 10% lumen increase produced by the translucent substrate).

FIG. 4a illustrates a cross-section view of an exemplary embodiment oflight emitting device 400. The light emitting device 400 includesseveral vertical LEDs 300 arranged on a substrate 420. The LED device400 of FIG. 4 is similar to the LED device 200 of FIG. 2 in that bothdevices include several LEDs arranged on a substrate. However, as willbe discussed, LED device 400 is designed to perform better than thelight emitting device 200 because to the inclusion of die attachmaterial 305 provides a higher light output.

Referring to FIG. 4a , as shown, the die attach material 305 is used tobond each of the LEDs 300 to the substrate 420. The substrate 420 mayinclude material similar to that of substrate 220 described with respectto FIG. 2a . Additionally, the die attach material covers at least aportion of the side walls of each of the vertical LEDs 300.

As discussed above, the die attach material 305 comprises a reflectivematerial such as white epoxy. As a result, light that is scattered bythe phosphor layer is reflected by the die attach material that wouldhave otherwise been absorbed by the vertical LED.

As illustrated in FIG. 4a , the die attach material increases lightoutput of the LED device 400 because light absorption between LEDs isreduced. Thus, more light is reflected away from adjacent vertical LEDsby the die attach material 305. In some aspects of the device, thisdesign increases light output by 10% lumen. Thus, the combination of atranslucent substrate and die attach material produces a light outputsimilar to the light output of conventional lateral LEDs, making thisdesign a suitable replacement for lateral LEDs in a chip-on-boardconfiguration.

FIG. 4b illustrates a top level view of an exemplary embodiment of thelight emitting device 400. The light emitting device 400 includessimilar features to those of light emitting device 200 described withrespect to FIG. 2b . For instance, the light emitting device 400includes an array of the vertical LEDs 300, the phosphor layer 440, andthe substrate 420. However, the light emitting device 400 additionallyincludes the reflective die attach material 305 that surrounds the sidewalls of each of the LEDs 300 in the array. Thus, greater light outputis realized by the light emitting device because the die attach materialprevents light that is scattered by phosphor layer 440 from beingabsorbed by the vertical LEDs 305.

FIG. 5a is a side view illustration of an exemplary lamp 500 having alight emitting device 502. Lamp 500 may be used for any type of generalillumination. For example, lamp 500 may be used in an automobileheadlamp, street light, overhead light, or in any other generalillumination application. The light emitting device 502 may be locatedin a housing 506. The light emitting device 502 may receive power via apower connection 504. The light emitting device 502 may be configured toemit light. Description pertaining to the process by which light isemitted by the light-emitting device 202 is provided with reference toFIG. 4.

FIG. 5b is a side view illustration of a flashlight 510, which is anexemplary embodiment of an apparatus having the light emitting device502. The light emitting device 502 may be located inside of the housing506. The flashlight 510 may include a power source. In some aspects ofthe light emitting device, the power source may include batteries 514located inside of a battery enclosure 512. In another aspect of thelight emitting device, power source 910 may be any other suitable typeof power source, such as a solar cell. The power connection 504 maytransfer power from the power source (e.g., the batteries 514) to thelight-emitting device 502.

FIG. 5c is a side view illustration of a street light 520, which isanother exemplary embodiment of an apparatus having the light emittingdevice 502. The light emitting device 502 may be located inside of thehousing 506. The street light 520 may include a power source. In someexemplary embodiments, the power source may include a power generator522. The power connection 504 may transfer power from the power source(e.g., the power generator 522) to the light emitting device 502.

The various aspects of this disclosure are provided to enable one ofordinary skill in the art to practice the present invention. Variousmodifications to exemplary embodiments presented throughout thisdisclosure will be readily apparent to those skilled in the art, and theconcepts disclosed herein may be extended to other devices. Thus, theclaims are not intended to be limited to the various aspects of thisdisclosure, but are to be accorded the full scope consistent with thelanguage of the claims. All structural and functional equivalents to thevarious components of the exemplary embodiments described throughoutthis disclosure that are known or later come to be known to those ofordinary skill in the art are expressly incorporated herein by referenceand are intended to be encompassed by the claims. Moreover, nothingdisclosed herein is intended to be dedicated to the public regardless ofwhether such disclosure is explicitly recited in the claims. No claimelement is to be construed under the provisions of 35 U.S.C. § 112(f)unless the element is expressly recited using the phrase “means for” or,in the case of a method claim, the element is recited using the phrase“step for.”

1-22. (canceled)
 23. A light emitting apparatus comprising: a basesubstrate; a vertical light emitting diode having one or more side wallsextending from the base substrate; and a reflective die attach materialsecuring the vertical light emitting diode to the base substrate andcovering at least a portion of an outer side of the one or more sidewalls of the vertical light emitting diode.
 24. The light emittingapparatus of claim 23, wherein the vertical light emitting diodecomprises a substrate and an active region configured to emit light,with the vertical light emitting diode disposed on the base substrateand the substrate of the vertical light emitting diode having the one ormore side walls that extend in a vertical direction orthogonal to thebase substrate.
 25. The light emitting apparatus of claim 24, whereinthe reflective die attach material extends in the vertical direction andcovers the portion of the outer side of the one or more side walls ofthe substrate of the vertical light emitting diode.
 26. The lightemitting apparatus of claim 24, wherein the substrate of the verticallight emitting diode is translucent or transparent to the light.
 27. Thelight emitting apparatus of claim 23, wherein the reflective die attachmaterial comprises white epoxy.
 28. The light emitting apparatus ofclaim 27, wherein the white epoxy comprises 10% greater light outputthan a silver epoxy.
 29. The light emitting apparatus of claim 23,wherein the reflective die attach material extends along at least halfof a height of the outer side of the one or more side walls.
 30. Thelight emitting apparatus of claim 23, wherein the vertical lightemitting diode comprises a gallium nitride layer over an aluminumnitride substrate.
 31. The light emitting apparatus of claim 30, furthercomprising a layer reflective disposed between the gallium nitride layerand the aluminum nitride substrate.
 32. The light emitting apparatus ofclaim 23, further comprising at least one additional light emitting diearranged on the base substrate and being configured to emit light. 33.The light emitting apparatus of claim 32, further comprising a phosphorlayer covering the vertical light emitting diode and the at least oneadditional light emitting die, wherein the phosphor layer is configuredto scatter the light.
 34. The light emitting apparatus of claim 33,wherein the reflective die attach material is configured to preventabsorption of the scattered light.
 35. A light emitting apparatuscomprising: a base substrate; a vertical light emitting diode disposedon the base substrate and having a carrier substrate that is translucentor transparent to light emitting by the vertical light emitting diodeand has one or more side walls extending from the base substrate; and areflective layer securing the vertical light emitting diode to the basesubstrate and covering at least a portion of an outer side of the one ormore side walls of the carrier substrate.
 36. The light emittingapparatus of claim 35, wherein the carrier substrate comprises aluminumnitride.
 37. A lamp comprising: a housing; a light emitting apparatuscoupled to the housing, the light emitting apparatus comprising: a basesubstrate; a plurality of vertical light emitting diodes that each haveone or more side walls extending from the base substrate; and areflective die attach material securing each of the vertical lightemitting diodes to the base substrate and covering at least a portion ofan outer side of the one or more side walls of each of the verticallight emitting diodes.
 38. The lamp of claim 38, further comprising amaterial over the plurality of vertical light emitting diodes to scatterthe light.
 39. The lamp of claim 38, wherein the light scatteringmaterial comprises phosphor.
 40. The lamp of claim 38, wherein thereflective die attach material is configured to prevent absorption ofthe scattered light between the plurality of vertical light emittingdiodes.
 41. The lamp of claim 37, wherein each of the plurality ofvertical light emitting diode comprises a substrate and an active regionconfigured to emit light, with the substrate of each vertical lightemitting diode having the one or more side walls that extend in avertical direction orthogonal to the base substrate.
 42. The lamp ofclaim 41, wherein the reflective die attach material extends in thevertical direction and completely covers the outer side of the one ormore side walls of each of the plurality of vertical light emittingdiodes only up to at most the active region of each of the plurality ofvertical light emitting diodes.
 43. The lamp of claim 41, wherein thesubstrate of the vertical light emitting diode is translucent ortransparent to the light.
 44. The lamp of claim 37, wherein thereflective die attach material comprises white epoxy.
 45. The lamp ofclaim 44, wherein the white epoxy comprises 10% greater light outputthan a silver epoxy.
 46. The lamp of claim 37, wherein each of thevertical light emitting diodes comprises a gallium nitride layer over analuminum nitride substrate.
 47. The lamp of claim 46, further comprisinga layer reflective disposed between the gallium nitride layer and thealuminum nitride substrate of each of the vertical light emittingdiodes.